1. Field of the Invention
This invention relates to an image information display apparatus, and more particularly to an apparatus for displaying several kinds of information related to each other in a plurality of display devices simultaneously.
2. Description of the Prior Art
In a microfilm system in which optical information such as characters, figures and the like is recorded on photographic recording materials in reduced scale, it is desirable that the information can be quickly retrieved and related several kinds of information can be displayed simultaneously or the display thereof can be quickly changed over.
One method of quickly changing over the display of related several kinds of information in a microfilm retrieval system is disclosed in Japanese patent publication No. 45-30306/70. In this method, two microfilms are arranged along the optical axis of a projection lens system of a microfilm projector. The two microfilms have related information and spaced apart from each other along the optical axis by the distance longer than the focal depth of the projection lens system, so that the image of only one of the films may be projected through the projection lens system. By quickly moving the projection lens along the optical axis thereof, the image projected therethrough is changed over.
Further, it is also known that two microfilms are arranged in an optical axis of a first projection lens system to be illuminated by the light of a light source and spaced apart from each other by the distance longer than the focal depth of the first projection lens system so that the image of one film may be projected therethrough, and a beam splitter is provided in the optical path to divide the light from the light source and a second projection lens system is provided in the optical path of the divided light to project the image of the other film therethrough.
The above described conventional method is disadvantageous in that the intensity of the illumination light for one film located within the focus of one projection lens system is reduced by the image of the other film located out of focus thereof. This results in undesirable uneven illumination on the projection screen. Particularly, in case that the film located out of focus has an image including bold characters, the image of the other film projected on the screen is markedly degraded by the shade thereof.